Two-neutron and core-excited states in Pb-210: Tracing E3 collectivity and evidence for a new beta-decaying isomer in Tl-210

Yrast and near-yrast levels up to an I = 17h spin value and a 6-MeV excitation energy have been delineated in the "two-neutron" ²¹⁰Pb nucleus following deep-inelastic reactions involving ²⁰⁸Pb targets and a number of heavy-ion beams at energies similar to 25% above the Coulomb barrier. The level scheme was established on the basis of multifold prompt and delayed coincidence relationships measured with the Gammasphere array. In addition to the previously known states, many new levels were identified. For most of the strongly populated states, spin-parity assignments are proposed on the basis of angular distributions. The reinvestigation of the nu(g9/2)², 8⁺ isomeric decay results in the firm identification of the low-energy E2 transitions involved in the 8⁺-> 6⁺-> 4⁺ cascade, and in a revised 6⁺ level half-life of 92(10) ns, nearly a factor of 2 longer than previously measured. Among the newly identified states figure spin I = 4-10 (h) over bar levels associated with the nu g9/2i11/2 multiplet, as well as yrast states involving nu g9/2j15/2, nu i11/2j15/2, and nu(j15/2)² neutron couplings. The highest-spin excitations are understood as 1p-lh core excitations and the yrast population is found to be fragmented to the extent that levels of spin higher than I = 17 (h) over bar could not be reached. Four E3 transitions are present in the ²¹⁰Pb yrast decay; three of these involve the g9/2-> j15/2 octupole component, as reflected in the 21(2) and > 10 Weisskopf unit enhancements of the B(E3) rates of the first two. The fourth, 16⁺-> 13^- E3 transition corresponds to the 3^- core octupole excitation built on the nu i11/j15/2 state, in analogy to a similar E3 coupling to the vj15/2 level in ²⁰⁹Pb. Shell-model calculations performed for two-neutron states and 1p-1h ²⁰⁸Pb core excitations are in good agreement with the data. Evidence was found for the existence of a hitherto unknown high-spin beta-decaying isomer in ²¹⁰Tl. Shell-model calculations of the ²¹⁰Tl levels suggest the possibility of a 11⁺ long-lived, j-decaying state, and the beta-delayed yields observed in various reactions fit rather well with a ²¹⁰Tl assignment.